1. Field of the Invention
The present invention relates to a pattern inspection apparatus and a pattern inspection method in which inspection is performed by reading a print pattern printed by a printer, and a printer in which a print pattern is printed and inspection is performed by reading the printed print pattern.
2. Description of the Related Art
Conventionally, an ink-jet printer is known, in which the printing is performed by discharging ink from a printing head carried on a carriage while reciprocatively moving the carriage in a scanning direction. In a certain ink-jet printer, ink is discharged from certain nozzles while moving a carriage in the scanning direction to thereby print a linear reference pattern extending in the main scanning direction. Subsequently, the recording paper P is transported by a certain distance, and then the ink is discharged from nozzles positioned on the downstream side in the transport direction as compared with the nozzles having been used to print the reference pattern, while moving the carriage in the scanning direction to thereby print an adjusting pattern extending linearly in the scanning direction. Accordingly, an error detecting print pattern, which is composed of the reference pattern and the adjusting pattern, is printed. The printing of the reference pattern and the adjusting pattern as described above is performed a plurality of times while changing the transport distance of the recording paper P, and thus a plurality of error detecting print patterns are printed. The plurality of error detecting print patterns are read by using an optical sensor to acquire densities of the respective error detecting print patterns. In this context, the density of the print pattern is the ratio of the areal size of the pattern portion to which the ink is adhered with respect to the areal size of the portion (white background portion) at which the recording medium is exposed. In this procedure, the acquired density is the lowest in relation to the error detecting print pattern in which the reference pattern and the adjusting pattern are overlapped to the greatest extent. Accordingly, in the ink-jet printer described above, the transport amount, which is provided when the error detecting print pattern having the lowest acquired density, is used as the transport amount to be used during the printing.
In relation thereto, in the case of the ink-jet printer in which the printing is performed by discharging the ink from the plurality of nozzles, any abnormality arises in a part of the reference pattern or the adjusting pattern, for example, such that a part of the reference pattern or the adjusting pattern is not printed and/or any dispersion arises in the thickness of the reference pattern or the adjusting pattern. For example, when the printing of the reference pattern and the adjusting pattern is repeatedly performed as in the ink-jet printer described above, the following situation sometimes arises. That is, the ink is not discharged upon the ink discharge performed for the first time during the printing of the reference pattern or the adjusting pattern performed for the first time, and a part of the reference pattern or the adjusting pattern is not printed. Further, the following situation sometimes arises. That is, the discharge speed and/or the volume of the ink discharged from the nozzles is/are fluctuated, and any dispersion arises in the thickness of the reference pattern or the adjusting pattern, on account of the temporarily unstable voltage supplied from a power source to the ink-jet printer, the vibration of the surface on which the ink-jet printer is arranged, and/or the change of the direction of the force applied to the ink contained in the ink-jet head during the acceleration or deceleration of the carriage depending on the movement direction of the carriage.
In this way, if any abnormality arises in a part of the reference pattern or the adjusting pattern, the density, which is acquired from the reading result obtained by reading the error detecting print pattern by means of the optical sensor, is consequently different from the density which is to be originally or normally acquired. As a result, it is feared that the error detecting print pattern, which includes any abnormal reference pattern or any abnormal adjusting pattern and which is different from the error detecting print pattern that is to originally have the lowest density, may be judged as the pattern which has the lowest density, and it is impossible to appropriately set the transport amount.